Question

Calcule a soma dos 10 primeiros termos da P.A(...,-2,23)

Answer 1

an=A1+(n-1).r
an=-2+(10-1).21
an=2+9.21
an=-2+189
an=187

Sn = (a1 + an) x n / 2
s10=(-2+187).10/2
s10=185.10/2
s10=1850/2
s10=925